Optical waveguide member and optical module

ABSTRACT

The present invention has an object of enhancing the tolerance of setup positioning error of an optical multiplexer/demultiplexer which uses a multi-mode optical waveguide. For this sake, the invention is designed to couple the multi-mode optical waveguide with a single-mode optical waveguide directly. In another configuration of this invention, there is provided between both optical waveguides a single-mode optical waveguide having its length set to be approximately equal to zero, or equal or approximately equal to the period of interference between the 0th-order mode and a radiative higher-order mode of the single-mode optical waveguide.

TECHNICAL FIELD

[0001] The present invention relates to an optical waveguide member andan optical module, and particularly to an opticalmultiplexer/demultiplexer and an optical module using the same.

BACKGROUND ART

[0002] Attention is paid to the wavelength division multiplexing (WDM)system from the viewpoint of enhanced speed and capacity of opticalcommunication. The optical multiplexer/demultiplexer is indispensabledevice for the WDM system. The devices in the type used by being coupledwith a single-mode fiber are particularly crucial. The reason is thatusing a single-mode fiber can transmit optical signals at lessdeterioration of signal waveform.

[0003] As a conventional device, there is known an optical demultiplexerdescribed in publication: Applied Physics Letter, Vol.61, No.15,pp.1754-1756, published in 1992, for example.

[0004]FIG. 13 is a plan view of a typical example of the device. Thisdevice is made up of a single-mode waveguide 10 of one core, amulti-mode waveguide 2, and a single-mode waveguide array 3 of fourcores, with all parts being coupled to series in the optical axisdirection on a substrate 1. When the device is used as demultiplexer, asingle-mode fiber 4 is coupled to the 1-core side and a light is put into the single-mode waveguide 10. The light excites in multiple modes atincidence to the multi-mode waveguide 2 and branches to four ways due tothe interference among the modes, and then is conducted from thesingle-mode waveguide array 3 to 4-core single-mode fibers 4′.

[0005] The above-said conventional device has its single-mode waveguide10 located between the 1-core single-mode fiber 4 and the multi-modewaveguide 2, so that the light is incident to the center of themulti-mode waveguide 2. In this case, however, if there is misalignmentbetween the single-mode fiber 4 and the device on its 1-core side, aradiative light 14 of a higher-order mode excites in the single-modewaveguide 10. This higher-order mode light 14 interferes with the0th-order mode light 13. Due to the fluctuation of light distributionduring the propagation, even a small misalignment can cause the incidentlight going into the multi-mode waveguide 2 to deviate greatly inposition and direction from the center axis. FIG. 14 shows the relationin this event among the center axis 11 of the single-mode fiber 4, thecenter axis 12 of the single-mode waveguide 10, and the peak positions15 of the light intensity. Other portions of this figure are referred toby the same symbols as those of FIG. 13. There arises a significantinequality in light output among the channels. Therefore, highpositioning accuracy is required in setting up the device, and it isdifficult to lower the setup cost based on a simple passive alignmentmethod.

[0006] In view of the foregoing situation, it is an object of thepresent invention to provide an optical multiplexer/demultiplexer whichhas large tolerance of setup positioning error against the single-modefiber and allows modular setup based on a low cost simple passivealignment method.

[0007] Japanese Patent Laid-Open No.H10(1998)-48458 describes an exampledirectly coupling of a multi-mode fiber to a multi-mode waveguide.However, this patent publication pertains solely to a technique of theuse of a multi-mode fiber.

DISCLOSURE OF THE INVENTION

[0008] A representative from of this invention is characterized bycoupling optically a multi-mode waveguide 2 and a 1-core single-modefiber 4 directly. The inventive optical waveguide member can be usedeither as optical multiplexer or as optical demultiplexer. Depending onas to whether the optical waveguide member is used as opticalmultiplexer or used as optical demultiplexer, it is different in lightinput direction. The inventive optical waveguide member can have theattachment of an optical device or optical elements at the input port oroutput port depending on the purpose.

[0009] The invention resides in an optical waveguide member which ischaracterized by comprising, at least, a multi-mode optical waveguideand a plurality of single-mode optical waveguides which are coupledoptically to a first end face of the multi-mode optical waveguide, themulti-mode optical waveguide being adapted to couple optically on itssecond end face, which is opposite to the first end face, with asingle-mode fiber.

[0010] It is significant for the inventive device to have the setting ofthe length of the single-mode optical waveguide which is coupledoptically to the second end face of the multi-mode optical waveguide.The manner of setting will be explained in detail later.

[0011] For the explanation of the principle of this invention, therelation between the length of 1-core single-mode waveguide and theinsertion loss will be exemplified. FIG. 15 shows a calculation resultof the relation between the length L_(IN) of 1-core single-modewaveguide and the insertion loss of the case of misalignment of 1.0 μmin the horizontal direction existing between the optical demultiplexerhaving a single-mode waveguide and the 1-core single-mode fiber 4. Thecalculation is based on the beam propagation method. The insertion losssignifies the optical loss attributable to the insertion of theinventive optical waveguide member on the light path.

[0012]FIG. 15 also shows the characteristics inherent to the typicaldevice structure of this invention, i.e., L_(IN)=0. Channels CH1 throughCH4 represent the characteristics of the 4-core single-mode opticalwaveguide. In this example, the outer single-mode optical waveguides CH1and CH4 are larger in insertion loss relative to other waveguides CH2and CH3. On the other hand, the characteristic graph reveals that theinequality of insertion loss among the channels becomes very small atcertain intervals of length. The inventive device adopts a structurewithout a 1-core single-mode optical waveguide or a structure with a1-core single-mode optical waveguide having such a waveguide length thatthe inequality of characteristics among the channels is very small. Itis appreciated that the inventive device structure can reduce theinequality of insertion loss among the channels, which is attributableto the positioning error in the horizontal direction between the opticaldemultiplexer having a single-mode waveguide and the 1-core single-modefiber 4, by about 5 dB from the worst-case value of the conventionaldevice. It is most desirable to couple optically the multi-modewaveguide 2 and the 1-core single-mode fiber 4 directly, as mentionedpreviously, which should be also affirmative from the viewpoints ofperformance and manufacturing.

[0013] The following explains the period of intervals at which theinequality of optical waveguide characteristics is minimal and variousforms of this invention.

[0014] As shown in FIG. 15, there are lengths L_(IN) in a period ofintervals of 200-250 μm at which the inequality of insertion loss amongthe channels virtually vanishes, besides the case where the lengthL_(IN) of 1-core single-mode waveguide is zero. This period is the beatlength of interference between the 0th-order mode 13 and radiativehigher-order mode 14 as shown in FIG. 14, and it is equal to a valuewhich is the value of π divided by the difference of propagationconstants of both modes.

[0015] Accordingly, the inventive device may have its length L_(IN) setto be an n-fold (n=0, 1, 2, . . . ) period of interference. This designscheme of an optical multiplexer/demultiplexer of the multi-modeinterference (MMI) type implies the comprehension of the radiation modein contrast to the conventional scheme which merely considers thewaveguide mode.

[0016] As a result of interference, the insertion loss among thechannels varies with the length L_(IN) periodically in a fashion oftrigonometric function. On this account, even if the value of L_(IN) isdifferent slightly from an n-fold value of interference period, theinequality of insertion loss among the channels can be minimized,whereby the intended characteristic can be attained.

[0017] Specifically, even with L_(IN) set within ⅕ of interferenceperiod, the object of this invention can be achieved adequately. Inother words, L_(IN) can be said virtually to be within ±40 μm. Accordingto this condition, the device is sufficiently applicable to moduleswhich are intended for the 10 Gb Ethernet for example.

[0018] Furthermore, L_(IN) can be set within a range from an n−⅕fold(n=0,1,2, . . . ) interference period to an n+⅕ fold interferenceperiod. In other words, L_(IN) can range within from ±40 μm to an n-fold(n=0,1,2, . . . ) value of interference period. Even in this case, theinequality of insertion loss among the channels can be reduced by about3 dB from the worst-case value of the conventional device.

[0019] More preferably, L_(IN) is set in a range within {fraction(1/10)} of the interference period. In other words, more preferably,L_(IN) is set within 20 μm.

[0020] Alternatively, the same effect can be attained by setting L_(IN)in a range from an n−{fraction (1/10)} fold (n=0,1,2, . . . )interference period to an n+{fraction (1/10)} fold interference period.In other words, more preferably, L_(IN) is made to range from an n-fold(n=0,1,2, . . . ) value of interference period to ±20 μm. In this case,the inequality of insertion loss among the channels can be expected todecrease by nearly 4 dB relative to the worst-case value of theconventional device.

[0021] Although the foregoing explanation is of the odd-numbered orderof a higher mode 14 which interferes with the 0th-order mode 13, theinterference period of the case of an even-numbered order is obtained asa value which is the value of 2π divided by the difference ofpropagation constants between the 0th-order mode 13 and a higher-ordermode 14.

[0022] In practicing this invention, it is optically desirable to havethe coincidence between the center axis of the multi-mode waveguide andthe center axis of the single-mode waveguide which is coupled opticallyto the second end face of the multi-mode waveguide. This configurationis common among the variant forms of this invention.

[0023] Although the foregoing explanation deals with the opticaldemultiplexer to exemplify the inventive optical waveguide member, theoptical multiplexer and demultiplexer have the same principle ofoperation, with only difference being their opposite light propagationdirections. Therefore, the inventive device when used as an opticalmultiplexer can secure a large tolerance of setup positioning error asin the case of the optical demultiplexer.

[0024] This invention is significant in terms of enabling theenhancement of the tolerance of setup positioning error of opticaldemultiplexer based on direct coupling of the single-mode fiber to themulti-mode waveguide.

BRIEF DESCRIPTION OF THE DRAWINGS

[0025]FIG. 1 is a plan view showing a first embodiment of thisinvention;

[0026]FIG. 2 is a plan view showing a second embodiment of thisinvention;

[0027]FIG. 3 is a perspective view showing one configuration the secondembodiment of this invention;

[0028]FIGS. 4A to 4C are partial cross-sectional diagrams showing thefabrication steps of the polymer optical waveguide section of the secondembodiment of this invention;

[0029]FIG. 5 is a plan view showing a third embodiment of thisinvention;

[0030]FIG. 6 is a plan view showing a fourth embodiment of thisinvention;

[0031]FIG. 7 is a plan view showing a fifth embodiment of thisinvention;

[0032]FIG. 8 is a plan view showing a sixth embodiment of thisinvention;

[0033]FIG. 9 is a plan view showing a seventh embodiment of thisinvention;

[0034]FIG. 10 is a plan view showing an eighth embodiment of thisinvention;

[0035]FIG. 11 is a plan view showing a ninth embodiment of thisinvention;

[0036]FIG. 12 is a plan view showing a tenth embodiment of thisinvention;

[0037]FIG. 13 is a plan view showing a conventional example;

[0038]FIG. 14 is a plan view showing the propagation of light in theconventional arrangement; and

[0039]FIG. 15 is a graph showing an example of the relation between thelength of single-mode waveguide in the 1-core side and the insertionloss.

PREFERRED MODE FOR CARRYING OUT THE INVENTION

[0040] The embodiments of this invention will be described.

[0041]FIG. 1 shows the first embodiment of this invention. The figure isa brief top view of the device. The device of this embodiment can beused as optical multiplexer and also as optical demultiplexer. In thisembodiment, a multi-mode waveguide 2 and a 4-core single-mode waveguidearray 3 are coupled optically on a substrate 1. The multi-mode waveguide2 has its another end face, which does not couple to the single-modewaveguide array 3, coupled optically with a single-mode fiber 4directly. On this account, this structure can minimize the inequality ofinsertion loss among the channels even in the presence of a positioningerror between the multi-mode waveguide 2 and the single-mode fiber 4 asdescribed previously. It is significant, as shown in this embodiment, tocouple the single-mode fiber directly to the multi-mode waveguide.

[0042]FIG. 2 shows the second embodiment of this invention. The figureis a brief top view of the device. This embodiment is an example ofoptical transmission module. Also in this embodiment, as in the firstembodiment, a multi-mode waveguide 2 and a 4-core single-mode waveguidearray 3 are coupled optically on a substrate 1. The multi-mode waveguide2 has its another end face, which does not couple with the single-modewaveguide array 3, coupled optically with a single-mode fiber 4directly. This module has a V-groove 6 formed in the substrate 1, whichis identical to that of the device of the first embodiment, therebypositioning and fixing the single-mode fiber 4 on the substrate 1. TheV-groove 6 is formed along the axial direction of the optical fiber. Thesubstrate 1 is, in general, a silicon substrate for example. TheV-groove, i.e., a groove with a V-shaped cross section, is formedprecisely by anisotropic etching of crystalline silicon. The groovestructure of crystalline silicon formed by anisotropic etching isusually called “V-groove”. In practice, however, there can be U shapesbesides the exact V shape and variations of these shapes. The term“V-groove” or “V-shape groove” used in this document of patentapplication comprehends all of these shapes of groove. Substratesthemselves having the V-shape groove structure are known in the art, anddetailed explanation thereof is omitted. There can be other means forthis purpose obviously.

[0043] In addition, the inventive device has the formation of a dicinggroove 7 for rectifying the end face of the V-groove 6. There are foursemiconductor lasers 5 of the distributed feedback (DFB) type havingdifferent oscillation wavelengths mounted on the substrate 1, which arecoupled optically with the single-mode waveguide array 3. The DFBsemiconductor lasers 5 are driven by being connected to a transmissionLSI 40 through wiring lines 41. This module is capable of multiplexinglights of different wavelengths generated by the four DFB semiconductorlasers 5 and conducting to the single-mode fiber 4 at a small loss and asmall inequality of loss among the channels. The module is alsooperative as a reception module by replacing the DFB semiconductorlasers with photodiodes of the waveguide type and replacing thetransmission LSI with a reception LSI. The module has large tolerance ofsetup positioning error in regard to the inequality of insertion lossamong the channels. It is significant also in this embodiment to couplethe single-mode fiber 4 directly to the multi-mode waveguide 2 asdescribed previously.

[0044]FIG. 3 shows by perspective view an example of fabrication of thepreceding second embodiment by use of a Si substrate and a polymerwaveguide. The portion of LSI is not shown in the figure. In thismodule, the multi-mode waveguide 2 and single-mode waveguide array 3shown in FIG. 2 are formed of a lower clad layer made of polymer (willbe termed “lower polymer clad layer”) 22, a core layer made of polymer(will be termed “polymer core layer”) 23, and an upper clad layer madeof polymer (will be termed “upper polymer clad layer”) 24. This polymerwaveguide is formed on a Si substrate 20 which is coated on its surfacewith a silicon dioxide film (will be termed “SiO₂ film”) 21. The rest isidentical to the second embodiment. Specifically, the optical fiber 4 isfitted by being positioned on the V-groove 6. A dicing groove 7 isformed to rectify the end face of the V-groove 6. Four-core single-modewaveguides 231,232,233 and 234 are connected to DFB semiconductor lasers51,52,53 and 54, respectively.

[0045] The module fabricated as described above attained the tolerancecharacteristic of positioning error of 1.0 μm or more against thesingle-mode fiber 4. Namely, the inequality among the channels is 0.5 dBor less. This example is for an operational wavelength band of 1.3 m.

[0046]FIG. 4 shows the fabrication process of the optical waveguidesection of the module described above. The usual fabrication processsuffices to make it. FIGS. 4A to 4C are cross-sectional diagrams of theprincipal portion of the waveguide, showing the sequential steps offabrication process.

[0047] For fabricating the optical waveguide, a Si substrate 20 on whichan SiO₂ film 21 is formed is prepared, and a lower polymer clad layer 22and polymer core layer 23 are formed on the SiO₂ film 21: (shown in FIG.4A). Next, the polymer core layer 23 is etched to leave portions incorrespondence to the 4-core single-mode waveguides 231,232,233 and 234:(shown in FIG. 4B) On the resulting substrate, an upper polymer cladlayer 24 is formed, and a polymer optical waveguide is completed:(shownin FIG. 4C). Typical polymer materials used in fabrication includepolyimide, polysiloxane, epoxy resin, acrylate resin, and fluorinatedpolymers of these resins.

[0048] The V-groove 6 of the silicon substrate 20 of the module can beformed by the anisotropic wet etching process which uses KOH solutionfor example.

[0049] In regard to the property of module for specific applications,the dimensions of optical waveguide core are about 6.5 μm by 6.5 μm, therefractivity of clad is about 1.525, the difference of refractivitybetween the clad and the core is around 0.4%-0.5%, for example. Thewavelength band used by this optical module is about from 1250 nm to1375 nm for example. Generally, four center wavelengths of 1257.7 nm,1300.2 nm, 1324.7 nm and 1349.2 nm are used for the 10 GbE-WWDM.

[0050] Although the foregoing explanation is of the case of use ofDFB-type semiconductor lasers or waveguide-type photodiodes,semiconductor lasers or photodiodes of other types or other opticalelements can be used depending on the requirement of individual opticalsystems.

[0051]FIG. 5 shows the third embodiment of this invention. Thisembodiment is an example which is derived from the second embodiment,with single-mode fibers 4, in place of the DFB semiconductor lasers 5,being coupled optically to the single-mode waveguide array 3. The restis identical to the preceding embodiments, and detailed explanation isomitted. This embodiment can be used as optical multiplexer or also asoptical demultiplexer. Moreover, in this embodiment, all or part of theoptical fibers which are coupled optically to the single-mode waveguidearray 3 may be replaced with multi-mode fibers. In this case, thisembodiment can be operated as optical demultiplexer.

[0052]FIG. 6 shows the fourth embodiment of this invention. The deviceof this embodiment is an example in which the substrate of opticalmodule is formed of multiple parts. Specifically, this example employs asecond substrate 8 which is separate from the substrate 1 on which themulti-mode waveguide 2 and single-mode waveguide array 3 are formed.Formed on the second substrate 8 is a second single-mode waveguide array9. The rest is identical to the embodiment of FIG. 5.

[0053] This embodiment is an example which is derived from the secondembodiment, with the second single-mode waveguide array 9, in place ofthe DFB semiconductor lasers 5, being coupled optically with thesingle-mode waveguide array 3. This embodiment can also be used asoptical multiplexer and also as optical demultiplexer. In case thedevice of this embodiment is used as optical demultiplexer, a multi-modewaveguide array or a waveguide array made up of multi-mode waveguidesand single-mode waveguides can be used in place of the single-modewaveguide array 9.

[0054]FIG. 7 shows the fifth embodiment of this invention. Thisembodiment is an example of optical multiplexer. This embodiment isderived from the optical module of the second embodiment, with thesingle-mode fiber 4 having its end face, which does not couple with themulti-mode waveguide 2, coupled to a multi-mode fiber 30. Thisarrangement enables the single mode from the single-mode fiber 4 to beincident to the center of the multi-mode fiber 30, whereby the waveguidemode can be roused efficiently in the multi-mode fiber 30. The rest isidentical to the embodiment of FIG. 2. As shown in this embodiment, thisinvention can be used effectively for optical transmission through amulti-mode fiber.

[0055] The inventive device can have an arbitrary number of single-modewaveguides of the single-mode waveguide array 3, instead of beingconfined to four waveguides which have been shown in the figures for theexplanation of the preceding embodiments. FIG. 8 shows, as the sixthembodiment, an example of module having seven single-mode waveguides.

[0056] The inventive device may be provided, between the multi-modewaveguide 2 and the single-mode fiber 4, with a single-mode waveguide 10having a finite length around 0 μm. FIG. 9 shows, as the seventhembodiment, an optical multiplexer/demultiplexer having such astructure. This embodiment can also have large tolerance of setuppositioning error as explained above. The above-mentioned “a finitelength around 0 μm” for the length of the single-mode waveguide 10 ismore specifically as explained in detail in the paragraph of Means forSolving the Problems. The allowable range of the length has beenexplained in connection with FIG. 15.

[0057] The following configurations of optical waveguide member arepractically useful. In one case, the single-mode waveguide in opticalcoupling with the second end face of the multi-mode waveguide has acenter value of the allowable range of length set equal to a value whichis the value of π divided by the difference of propagation constantsbetween the 0th-order eigen mode and the radiative first-order mode ofthe single-mode waveguide. In another case, the single-mode waveguide inoptical coupling with the second end face of the multi-mode waveguidehas a center value of the allowable range of length set equal to a valuewhich is the value of 2π divided by the difference of propagationconstants between the 0th-order eigenmode and the radiative second-ordermode of the single-mode waveguide. Optical modules using these opticalwaveguide members are useful.

[0058] It is desirable practically for these optical waveguide membersto be configured such that the center axis of the multi-mode waveguideis coincident with the center axis of the single-mode waveguide which iscoupled optically to the second end face of the multi-mode waveguide.

[0059]FIG. 10 shows the eighth embodiment of this invention. Thisembodiment is an example of transmission module or reception modulebased on the device of the previous seventh embodiment. With thesingle-mode waveguide array 3 being coupled with single-mode fibers orsingle-mode waveguides in place of optical elements, the module can beoperative as optical multiplexer/demultiplexer.

[0060] The inventive device may be provided, between the multi-modewaveguide 2 and the single-mode fiber 4, with a single-mode waveguide 10having its length set to be equal or approximately equal to the periodof interference between the 0th-order mode and a radiative higher-ordermode. FIG. 11 shows the ninth embodiment having this structure. Thiscase also can have large tolerance of setup positioning error asexplained above. The specific length of the single-mode waveguide 10 isas explained in detail in the paragraph of Means for Solving theProblems.

[0061]FIG. 12 shows the tenth embodiment of this invention. Thisembodiment is an example of transmission module or reception modulebased on the device of the previous ninth embodiment.

[0062] With the single-mode waveguide array 3 being coupled withsingle-mode fibers or single-mode waveguides in place of opticalelements, the module can be operative as opticalmultiplexer/demultiplexer.

[0063] This invention is effective regardless of the materials of thesubstrate, waveguides and other constituents, and is not confined to thecases explained in the foregoing embodiments. In addition, thisinvention is effective regardless of the positioning and fixing mannersof the single-mode fiber, optical elements, waveguides, and otherconstituents, and is not confined to the cases explained in theforegoing embodiments.

[0064] The following itemizes various cases of the length of thesingle-mode optical waveguide which is coupled optically to the secondend face of the multi-mode waveguide. Cases represented solely in termsof specific numerals, such as 20 μm or less, or 40 μm or less, areexcluded.

[0065] (1) In an optical waveguide member including a multi-mode opticalwaveguide, a plurality of first single-mode optical waveguides which arecoupled optically to a first end face of the multi-mode opticalwaveguide, and at least one second single-mode waveguide which iscoupled optically to a second end face, which is opposite to the firstend face, of the multi-mode optical waveguide, the second single-modeoptical waveguide has a length which is at least in any of a range(positive number) from n−⅕ fold to n+⅕ fold values (where n=0,1,2, . . .) of the period of interference between the 0th-order eigenmode and aradiative higher-order mode of the second single-mode waveguide, a range(positive number) from n−⅕ fold to n+⅕ fold values (where n=0,1,2, . . .) of a value which is the value of π divided by the difference ofpropagation constants between the 0th-order eigen mode and a radiativehigher-order mode of the second single-mode waveguide, and a range(positive number) from n−⅕ fold to n+⅕ fold values (where n=0, 1,2, . .. ) of a value which is the value of 2π divided by the difference ofpropagation constants between the 0th-order eigen mode and a radiativehigher-order mode of the second single-mode waveguide.

[0066] (2) In an optical waveguide member set forth in item (1), theabove-said single-mode waveguide which is coupled optically to thesecond end face of the multi-mode waveguide has a length which ranges(positive number) from n−{fraction (1/10)} fold to n+{fraction (1/10)}fold values (where n=0, 1, 2, . . . ) of the period of interferencebetween the 0th-order eigen mode and a radiative higher-order mode ofthe above-said single-mode waveguide.

[0067] (3) In an optical waveguide member including, at least, amulti-mode optical waveguide, a plurality of single-mode opticalwaveguides which are coupled optically to a first end face of themulti-mode optical waveguide, a single-mode optical waveguide which iscoupled optically to a second end face, which is opposite to the firstend face, of the multi-mode optical waveguide, and a single-mode fiberwhich is coupled optically to a second end face, which is opposite to afirst end face coupled to the multi-mode optical waveguide, of thesingle-mode optical waveguide, the above-said single-mode opticalwaveguide has a length which ranges (positive number) from an n-foldvalue (where n=0, 1, 2, . . . ) of the period of interference betweenthe 0th-order eigen mode and a radiative higher-order mode of theabove-said single-mode waveguide to ±40 μm.

[0068] (4) In an optical waveguide member set forth in item (4) theabove-said single-mode waveguide which is coupled optically to thesecond end face of the multi-mode waveguide has a length which ranges(positive number) from an n-fold value (where n=0,1,2, . . . ) of theperiod of interference between the 0th-order eigen mode and a radiativehigher-order mode of the above-said single-mode waveguide to ±20 μm.

[0069] (5) In an optical waveguide member including, at least, amulti-mode optical waveguide, a plurality of single-mode opticalwaveguides which are coupled optically to a first end face of themulti-mode optical waveguide, a single-mode waveguide which is coupledoptically to a second end face, which is opposite to the first end face,of the multi-mode optical waveguide, and a single-mode fiber which iscoupled optically to a second end face, which is opposite to a first endface coupled to the multi-mode optical waveguide, of the single-modeoptical waveguide, the above-said single-mode optical waveguide has alength which ranges (positive number) from n−⅕ fold to n+⅕ fold values(where n=0,1,2, . . . ) of a value which is the value of π divided bythe difference of propagation constants between the 0th-order eigenmodeand a radiative higher-order mode of the above-said single-modewaveguide.

[0070] (6) In an optical waveguide member set forth in item (5) theabove-said single-mode waveguide which is coupled optically to thesecond end face of the multi-mode waveguide has a length which ranges(positive number) from n−{fraction (1/10)} fold to n+{fraction (1/10)}fold values (where n=0,1,2, . . . ) of a value which is the value of πdivided by the difference of propagation constants between the 0th-ordereigenmode and a radiative higher-order mode of the above-saidsingle-mode waveguide.

[0071] (7) In an optical waveguide member including, at least, amulti-mode optical waveguide, a plurality of single-mode opticalwaveguides which are coupled optically to a first end face of themulti-mode optical waveguide, and a second single-mode waveguide whichis coupled optically to a second end face, which is opposite to thefirst end face, of the multi-mode optical waveguide, the above-saidsingle-mode optical waveguide is adapted to couple optically on itssecond end face, which is opposite to the first end face in couplingwith the multi-mode optical waveguide, with a single-mode fiber, and theabove-said single-mode optical waveguide has a length which ranges(positive number) from a value which is the value of π divided by thedifference of propagation constants between the 0th-order eigenmode anda radiative higher-order mode of the above-said single-mode waveguide to±40 μm.

[0072] (8) In an optical waveguide member, the above-said single-modewaveguide which is coupled optically to the second end face of themulti-mode waveguide has a length which ranges (positive number) from avalue which is the value of π divided by the difference of propagationconstants between the 0th-order eigenmode and a radiative higher-ordermode of the above-said single-mode waveguide to ±20 μm.

[0073] (9) In an optical waveguide member including, at least, amulti-mode optical waveguide, a plurality of single-mode opticalwaveguides which are coupled optically to a first end face of themulti-mode optical waveguide, and a single-mode waveguide which iscoupled optically to a second end face, which is opposite to the firstend face, of the multi-mode optical waveguide, the above-saidsingle-mode optical waveguide is adapted to couple optically on itssecond end face, which is opposite to the first end face in couplingwith the multi-mode optical waveguide, with a single-mode fiber, and theabove-said single-mode optical waveguide has a length which ranges(positive number) from n−⅕ fold to n+⅕ fold values (where n=0, 1,2, . .. ) of a value which is the value of 2π divided by the difference ofpropagation constants between the 0th-order eigenmode and a radiativehigher-order mode of the above-said single-mode waveguide.

[0074] (10) In an optical waveguide member, the above-said single-modewaveguide which is coupled optically to the second end face of themulti-mode waveguide has a length which ranges (positive number) fromn−{fraction (1/10)} fold to n+{fraction (1/10)} fold values (wheren=0,1,2, . . . ) of a value which is the value of 2π divided by thepropagation constants between the 0th-order eigenmode and a radiativehigher-order mode of the above-said single-mode waveguide.

[0075] (11) In an optical waveguide member including, at least, amulti-mode optical waveguide, a plurality of single-mode opticalwaveguides which are coupled optically to a first end face of themulti-mode optical waveguide, and a single-mode waveguide which iscoupled optically to a second end face, which is opposite to the firstend face, of the multi-mode optical waveguide, the above-saidsingle-mode optical waveguide is adapted to couple optically on itssecond end face, which is opposite to the first end face in couplingwith the multi-mode optical waveguide, with a single-mode fiber, and theabove-said single-mode optical waveguide has a length which ranges(positive number) from a value which is the value of 2π divided by thedifference of propagation constants between the 0th-order eigenmode anda radiative higher-order mode of the above-said single-mode waveguide to±40 μm.

[0076] (12) In an optical waveguide member set forth in item (11) theabove-said single-mode waveguide which is coupled optically to thesecond end of the multi-mode waveguide has a length which ranges(positive number) from a value which is the value of 2π divided by thedifference of propagation constants between the 0th-order eigenmode anda radiative higher-order mode of the above-said single-mode waveguide to±20 μm.

[0077] The following itemizes practical configurations of the inventiveoptical waveguide member.

[0078] Firstly, the inventive optical waveguide member is characterizedby having at least one of its multi-mode waveguide and single-modewaveguide formed of a material of polymer.

[0079] Secondly, the inventive optical waveguide member is characterizedby having at least one of its multi-mode waveguide and single-modewaveguide formed on a silicon substrate.

[0080] Thirdly, the inventive optical waveguide member is characterizedby having its single-mode optical waveguide coupled optically on one endface thereof, which is different from another end face in coupling withthe multi-mode waveguide, with a single-mode fiber.

[0081] Fourthly, the single-mode fiber is fixed by means of a V-shapegroove or a groove of other cross-sectional shape formed in thesubstrate which is shared with the multi-mode waveguide or single-modewaveguides.

[0082] Fifthly, the inventive optical waveguide member is characterizedin that the single-mode fiber is coupled optically on its end face,which does not couple optically with neither the single-mode waveguidenor the multi-mode waveguide, with a multi-mode fiber. It is desirablethat the technical concept of the invention be applied to the third andfourth items.

[0083] The following itemizes examples of optical module of this patentapplication.

[0084] A first configuration of optical module comprises at least oneoptical multiplexer or optical demultiplexer of this invention, and ischaracterized in that at least one of the single-mode waveguides, whichare coupled optically to a first end face of the multi-mode waveguideincluded in the optical multiplexer or optical demultiplexer, is coupledoptically on its end face, which does not couple optically with themulti-mode waveguide, with a single-mode fiber or multi-mode fiber.

[0085] A second configuration of optical module is derived from thefirst configuration, and is characterized in that the single-mode fiberor multi-mode fiber, which is coupled optically to the single-modewaveguide in optical coupling with the first end face of the multi-modewaveguide, is fixed by means of a V-shape groove or a groove of othercross-sectional shape formed in the substrate which is shared with themulti-mode waveguide or single-mode waveguides.

[0086] A third configuration of optical module is derived from the firstconfiguration, and is characterized in that semiconductor lasers of thedistribution feedback type or distribution reflection type havingdifferent oscillation wavelengths are coupled optically to thesingle-mode waveguides which are coupled optically to the first end faceof the multi-mode waveguide of the optical multiplexer.

[0087] A fourth configuration of optical module is derived from thefirst configuration, and is characterized in that photodiodes of thewaveguide type are coupled optically to the single-mode waveguides whichare coupled optically to the first end face of the multi-mode waveguideof the optical demultiplexer.

[0088] Using the inventive optical waveguide members and elementsenables the setup of module based on the inexpensive passive alignmentscheme, whereby a low-cost optical module can be accomplished.

[0089] According to the embodiments of this invention, there areprovided optical waveguide members, e.g., opticalmultiplexer/demultiplexer, having large tolerance of setup positioningerror.

[0090] Capability of Industrial Application

[0091] This invention resides in an optical waveguide member which ischaracterized by including a multi-mode optical waveguide and aplurality of first single-mode optical waveguides which are coupledoptically to a first end face of the multi-mode optical waveguide, withthe multi-mode waveguide being adapted to couple optically on its secondend face, which is opposite to the first end face, with a single-modefiber, and the invention can provide optical waveguide members, e.g.,optical multiplexer/demultiplexer, having large tolerance of setuppositioning error.

1. An optical waveguide member comprising: at least, a multi-modeoptical waveguide and a plurality of first single-mode opticalwaveguides which are coupled optically to a first end face of saidmulti-mode optical waveguide, said multi-mode optical waveguide adaptedto couple optically on a second end face thereof, which is opposite tothe first end face, with a single-mode fiber.
 2. An optical waveguidemember set forth in claim 1 characterized by including, at least, asingle-mode fiber which is coupled optically to the second end face,which is opposite to the first end face, of said multi-mode opticalwaveguide.
 3. An optical waveguide member set forth in claim 1, whereinat a position contiguous to the second end face of said multi-modeoptical waveguide, a groove structure for holding an optical fiber to becoupled optically to the second end face of said multi-mode opticalwaveguide is set.
 4. An optical waveguide member set forth in claim 2,wherein at a position contiguous to the second end face of saidmulti-mode optical waveguide, a groove structure for holding an opticalfiber to be coupled optically to the second end face of said multi-modeoptical waveguide is set, including a single-mode fiber which is coupledoptically to the second end face of said multi-mode optical waveguide,and having said single-mode fiber held by means of said groovestructure.
 5. An optical waveguide member set forth in claim 1, whereinat least one of said multi-mode optical waveguide and said firstsingle-mode optical waveguides is formed of a material of polymer resin.6. An optical waveguide member set forth in claim 2, wherein at leastone of said multi-mode optical waveguide and said first single-modeoptical waveguides is formed of a material of polymer resin.
 7. Anoptical waveguide member set forth in claim 1, wherein at least one ofsaid multi-mode optical waveguide and said first single-mode opticalwaveguides is formed on a silicon substrate.
 8. An optical waveguidemember set forth in claim 2, wherein at least one of said multi-modeoptical waveguide and said first single-mode optical waveguides isformed on a silicon substrate.
 9. An optical module comprising: at leastone of the optical waveguide member set forth in claim 2, and at leastone of a plurality of first single-mode optical waveguides which arecoupled optically to the first end face of the multi-mode opticalwaveguide included in said optical waveguide member, and on the secondend face, which does not couple optically with said multi-mode opticalwaveguide, of said multi-mode optical waveguide, at least one memberselected from a group of an optical element, an optical waveguide, asingle-mode fiber and a multi-mode fiber which are coupled opticallywith the second end face of said multi-mode optical waveguide, and agroove structure for holding an optical fiber.
 10. An optical waveguidemember comprising: at least, a multi-mode optical waveguide, a pluralityof first single-mode optical waveguides which are coupled optically to afirst end face of said multi-mode optical waveguide, and at least onesecond single-mode optical waveguide which is coupled optically to asecond end face, which is opposite to the first end face, of saidmulti-mode optical waveguide, said second single-mode waveguide having alength of 40 μm or less.
 11. An optical waveguide member set forth inclaim 10, wherein said at least one second single-mode optical waveguidehas a third and fourth end faces, the third end face of said secondsingle-mode optical waveguide being coupled optically to the second endface of said multi-mode optical waveguide, said member including asingle-mode fiber which is coupled optically to the fourth end facewhich is opposite to the third end face in coupling with said multi-modeoptical waveguide.
 12. An optical waveguide member set forth in claim10, wherein said at least one second single-mode optical waveguide has athird and fourth end faces, the third end face of said secondsingle-mode optical waveguide being coupled optically to the second endface of said multi-mode optical waveguide, said at least one secondsingle-mode optical waveguide having a length of 20 μm or less.
 13. Anoptical waveguide member set forth in claim 12, wherein a single-modefiber which is coupled optically to said fourth end face of said atleast one second single-mode optical waveguide.
 14. An optical waveguidemember set forth in claim 10, wherein said at least one secondsingle-mode optical waveguide has a third and fourth end faces, saidthird end face of said second single-mode optical waveguide beingcoupled optically to the second end face of said multi-mode opticalwaveguide, and at a position contiguous to said fourth end face of saidsecond single-mode optical waveguide, a groove structure for holding anoptical fiber to be coupled optically to the fourth end face is set. 15.An optical waveguide member set forth in claim 11, wherein at a positioncontiguous to said fourth end face of said second single-mode opticalwaveguide, a groove structure for holding an optical fiber to be coupledoptically to the fourth end face is set, and having a single-mode fiberwhich is coupled optically to the fourth end face of said multi-modeoptical waveguide, and said single-mode fiber is held by means of saidgroove structure.
 16. An optical waveguide member set forth in claim 12,wherein at a position contiguous to said fourth end face of said secondsingle-mode optical waveguide, a groove structure for holding an opticalfiber to be coupled optically to the fourth end face is set.
 17. Anoptical waveguide member set forth in claim 10, wherein at least one ofsaid multi-mode optical waveguide and said first and second single-modeoptical waveguides is formed of a material of polymer resin.
 18. Anoptical waveguide member set forth in claim 10, wherein at least one ofsaid multi-mode optical waveguide and said first and second single-modeoptical waveguides is formed on a silicon substrate.
 19. An opticalwaveguide member comprising: a multi-mode optical waveguide, a pluralityof first single-mode optical waveguides which are coupled optically to afirst end face of said multi-mode optical waveguide, and at least onesecond single-mode optical waveguide which is coupled optically to asecond end face, which is opposite to the first end face, of saidmulti-mode optical waveguide, wherein said second single-mode waveguidehas a length which is at least in any of a range (positive number) fromn−⅕ fold to n+⅕ fold values (where n=0,1,2, . . . ) of the period ofinterference between the 0th-order eigenmode and a radiativehigher-order mode of said second single-mode waveguide, a range(positive number) from n−⅕ fold to n+⅕ fold values (where n=0, 1, 2, . .. ) of a value which is the value of π divided by the difference ofpropagation constants between the 0th-order eigenmode and a radiativehigher-order mode of said second single-mode waveguide, and a range(positive number) from n−⅕ fold to n+⅕ fold values (where n=0,1,2, . . .) of a value which is the value of 2π divided by the difference ofpropagation constants between the 0th-order eigenmode and a radiativehigher-order mode of said second single-mode waveguide.
 20. An opticalwaveguide member set forth in claim 19, wherein said at least one secondsingle-mode optical waveguide has a third and fourth end faces, thethird end face of said second single-mode optical waveguide beingcoupled optically to the second end face of said multi-mode opticalwaveguide, said optical waveguide member including a single-mode fiberwhich is coupled optically to the fourth end face, which is opposite tothe second end face in coupling with said multi-mode optical waveguide,of said single-mode optical waveguide.